Method for calibrating nuclear magnetism T2 distribution of strong heterogeneous carbonate rock fractures

Abstract

The invention discloses a method for calibrating nuclear magnetism T2 distribution of strong heterogeneity carbonate rock fractures, which comprises the steps of total porosity calculation, saturated state rock sample scanning, critical state rock sample construction, critical state rock sample scanning, fracture aperture distribution extraction, T2-r conversion relation establishment and the like. According to the method, the distribution position and content of the cracks can be effectively extracted, compared with an existing method, the precision of quantitative characterization of the cracks through the nuclear magnetism technology is improved, and a reliable basis is provided for evaluation of the strong heterogeneous carbonate rock crack structure with a large number of developed cracks.

Description

Technical Field

[0001] The present invention relates to the technical field of carbonate oil and gas exploitation, and particularly relates to a method for calibrating the nuclear magnetic T2 distribution of fractures in strongly heterogeneous carbonate rocks. Background Art

[0002] Carbonate oil and gas reservoirs play an extremely important role in the global oil and gas resources. Their oil and gas resources account for about 70% of the global oil and gas resources, recoverable reserves account for about 50%, and production accounts for about 60%. Carbonate oil and gas reservoirs have the characteristics of complex pore structures and strong heterogeneity. Fractures are the main storage spaces and migration channels of such oil and gas reservoirs. Clearly defining the fracture distribution characteristics is the key issue for carbonate reservoir evaluation. At present, carbonate fracture evaluation methods are mainly divided into two categories: 1) direct observation methods, such as optical microscopes, scanning electron microscopes, etc., and the observation results are two-dimensional images and semi-quantitative; 2) indirect observation methods, and the main observation means include mercury injection, nuclear magnetic resonance (NMR), and CT scanning, etc., and the test results are quantitative pore size distribution curves. The pores of small plunger samples (diameter 2.5 cm) show homogeneity, and the representativeness of fracture evaluation results is poor; large-sized rock samples (length 5 - 7 cm, diameter 6 cm or 10 cm) have strong representativeness and are the first choice for studying the pore and fracture characteristics of strongly heterogeneous carbonate rocks.

[0003] Among the above methods, only NMR and CT can achieve non-destructive testing of full-diameter samples, and NMR is the only method that can carry out downhole continuous testing (nuclear magnetic resonance logging).

[0004] The intensity of the X-ray emitted by the CT instrument after penetrating an object is related to the density of the object. By analyzing the number of pixels or CT numbers in the scanned image, the basic information of the skeletal particles and pore fractures in the rock can be obtained. The pores are approximately spherical, and the fractures are long and narrow. Usually, pores with a ratio of major axis to minor axis greater than 5 - 10 (the size is related to the formation) are defined as fractures. Based on this, the CT technology can further divide the pores into matrix pores and fractures. CT can accurately identify fractures in full-diameter cores, but the sample size is inversely proportional to the CT resolution, and using full-diameter samples will lose some matrix pores.

[0005] The nuclear magnetic resonance T2 time is proportional to the pore radius r. This technology uses the proportion of fluids filling different pores to obtain the distribution characteristics of pores of different sizes. For formations with poor fracture development and high pore-fracture differentiation, the fracture distribution interval can be more accurately judged according to the T2 spectrum morphology. However, for strongly heterogeneous formations with a large number of fractures, the differentiation between matrix pores and fractures is very poor, and the existing NMR methods cannot accurately and quantitatively distinguish matrix pores and fractures. Summary of the Invention

[0006] Aiming at the problem that it is difficult for existing NMR methods to accurately quantify the fracture distribution in strongly heterogeneous carbonate rocks, the present invention, based on the NMR of full-diameter samples and micro-CT scanning technology, proposes a method for calibrating the nuclear magnetic T2 distribution of fractures in strongly heterogeneous carbonate rocks, which can effectively extract the distribution position and content of fractures, improve the accuracy of quantitative characterization of fractures using nuclear magnetic technology, and provide a reliable basis for the evaluation of the fracture structure of strongly heterogeneous carbonate rocks with a large number of developed fractures.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A method for calibrating the nuclear magnetic T2 distribution of fractures in strongly heterogeneous carbonate rocks, comprising:

[0009] Calculation of total porosity: Select several carbonate rocks with developed fractures and prepare rock samples, and calculate the total porosity of the rock samples based on the mass difference between the dry-state rock samples and the saturated-state rock samples

[0010] Scanning of saturated-state rock samples: Obtain the T2 spectrum of the saturated-state rock samples based on nuclear magnetic resonance scanning, denoted as T2 A , scan the saturated-state rock samples by CT and draw the pore size r distribution spectrum, denoted as CT A ;

[0011] Construction of critical-state rock samples: Construct critical-state rock samples based on the gas displacement experiment with water, and extract the evaluation parameters of the critical-state rock samples;

[0012] Scanning of critical-state rock samples: Obtain the T2 spectrum of the critical-state rock samples based on nuclear magnetic resonance scanning, denoted as T2 B , scan the critical-state rock samples by CT and draw the pore size r distribution spectrum, denoted as CT B ;

[0013] Extraction of fracture pore size distribution: Based on the T2 spectrum difference and pore size r distribution spectrum difference between the saturated-state rock samples and the critical-state rock samples, respectively obtain the T2 time distribution of fracture pore size T2 A -T2 B , the fracture pore size dimension r distribution CT A -CT B ;

[0014] Establishment of T2-r conversion relationship: Based on the graphical six-point coupling method, match the CT A -CT B histogram with the T2 A -T2 B graph to establish a quantitative T2-r pore size conversion relationship formula, and obtain the nuclear magnetic T2 distribution of matrix pores and fractures.

[0015] Furthermore, the calculation of the total porosity includes:

[0016] Sample preparation: Select several carbonate rocks with developed fractures and prepare rock samples;

[0017] Drying: Dry the rock samples and let them stand until room temperature, then weigh the dry weight m d , and measure the total volume V b ;

[0018] Saturation weighing: After evacuating the rock samples, apply pressure and inject a saturated potassium iodide aqueous solution. After a period of time, weigh the mass m of the rock samples in the saturated state s ;

[0019] Calculation of total porosity: Calculate the total porosity based on the mass difference between the rock samples in the dry state and the saturated state where ρ is the density of the aqueous solution.

[0020] Furthermore, during the scanning of the rock samples in the saturated state:

[0021] The T2 spectrum obtained by nuclear magnetic resonance scanning of the rock samples in the saturated state, i.e., T2 A reflects the distribution of all pores, including non-matrix pores and all matrix pores;

[0022] CT scan the rock samples in the saturated state and draw the pore size r distribution spectrum, i.e., CT A reflects the pore distribution above the resolution of the CT scanner, including non-matrix pores and some matrix pores.

[0023] Furthermore, the non-matrix pores are fractures, and the matrix pores include the first type of matrix pores and the second type of matrix pores. The first type of matrix pores represent the matrix pores lost due to being below the resolution of the CT scanner, and the second type of matrix pores represent the matrix pores identified by the CT scanner.

[0024] Furthermore, the scanning of the rock samples in the saturated state also includes:

[0025] Calculate the CT porosity based on the pore size r distribution spectrum

[0026] Distinguish pores and fractures based on CT image recognition technology and calculate the porosity of the second type of matrix pores and the fracture porosity where

[0027] Furthermore, during the construction of the rock samples in the critical state, the critical state refers to the state where only the matrix pores of the rock samples contain water, and the non-matrix pores where the fractures are located do not contain water.

[0028] Furthermore, the construction of the rock samples in the critical state includes:

[0029] Calculation of water saturation: Combine the total porosity of the rock samples and the fracture porosity Calculate the water saturation of rock samples in the critical state

[0030] Critical state evaluation: According to the water saturation S of rock samples in the critical state C Calculate the critical mass of water m C =(m s -m d )*(1 - S C ), where m d is the mass of the rock sample in the dry state, and m s is the mass of the rock sample in the saturated state; After placing the rock sample in the holder, apply confining pressure to wrap it, place a graduated cylinder at the outlet end of the holder to collect the water discharged from the pores, and stop the water displacement experiment with gas when the water output reaches the critical mass m C , otherwise continue the water displacement experiment with gas.

[0031] Furthermore, during the scanning of the saturated state rock sample:

[0032] The T2 spectrum obtained by nuclear magnetic resonance scanning of the rock sample in the critical state, namely T2 B reflects the pore distribution of the first type of matrix pores and the second type of matrix pores;

[0033] CT scan the rock sample in the critical state and draw the pore size r distribution spectrum formed, namely CT B reflects the pore distribution of the second type of matrix pores.

[0034] Furthermore, the extraction of the fracture pore size distribution includes:

[0035] Based on the differential spectrum method, subtract the pore size r distribution spectra of the saturated state rock sample and the critical state rock sample to obtain the fracture pore size r distribution CT A -CT B , and then convert it into a bar chart of the fracture pore size distribution;

[0036] Based on the differential spectrum method, subtract the T2 spectra of the saturated state rock sample and the critical state rock sample to obtain the fracture pore size T2 time distribution T2 A -T2 B .

[0037] Furthermore, the establishment of the T2 - r conversion relationship includes:

[0038] Based on the graphical six - point coupling method, match the CT A -CT B bar chart with the T2 A -T2 B to extract 6 cross - point (T2, r) data and establish a quantitative T2 - r pore size conversion relationship;

[0039] Under the same coordinate system, the nuclear magnetic resonance T2 distributions of matrix pores and fractures are plotted respectively, and the pore diameter r value is marked at the abscissa.

[0040] The beneficial effects of the present invention are as follows:

[0041] Aiming at the problem that the nuclear magnetic resonance T2 spectrum is difficult to effectively identify fractures in strongly heterogeneous carbonate rocks, the present invention proposes a method for calibrating the nuclear magnetic resonance T2 distribution of fractures in strongly heterogeneous carbonate rocks, which can effectively extract the distribution position and content of fractures. Compared with the existing methods, the accuracy of quantitative characterization of fractures by nuclear magnetic resonance technology is improved, providing a reliable basis for the evaluation of the fracture structure of strongly heterogeneous carbonate rocks with a large number of developed fractures. Description of the Drawings

[0042] Figure 1 It is a flow chart of the method for calibrating the nuclear magnetic resonance T2 distribution of fractures in strongly heterogeneous carbonate rocks according to an embodiment of the present invention.

[0043] Figure 2 It is a relationship model between CT porosity and total porosity according to an embodiment of the present invention. Detailed Embodiments

[0044] For a clearer understanding of the technical features, objectives, and effects of the present invention, the detailed embodiments of the present invention are now described. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0045] This embodiment provides a method for calibrating the nuclear magnetic resonance T2 distribution of fractures in strongly heterogeneous carbonate rocks, including:

[0046] Calculation of total porosity: Select several carbonate rocks with developed fractures and prepare rock samples, and calculate the total porosity of the rock samples based on the mass difference between the dry-state rock samples and the saturated-state rock samples

[0047] Scanning of saturated-state rock samples: Based on nuclear magnetic resonance scanning of saturated-state rock samples, obtain the T2 spectrum denoted as T2 A , perform CT scanning on the saturated-state rock samples and plot the pore diameter r distribution spectrum denoted as CT A ;

[0048] Construction of critical-state rock samples: Based on the gas displacement experiment, construct critical-state rock samples and extract the evaluation parameters of the critical-state rock samples;

[0049] Scanning of critical-state rock samples: Based on nuclear magnetic resonance scanning of critical-state rock samples, obtain the T2 spectrum denoted as T2 B, CT scan the rock samples in the critical state and record the pore size r distribution spectrum as CT B ;

[0050] Fracture pore size distribution extraction: Based on the difference between the T2 spectra of the saturated state rock samples and the critical state rock samples, and the difference between the pore size r distribution spectra, obtain the T2 time distribution T2 of the fracture pore size A -T2 B and the r distribution CT of the fracture pore size A -CT B ;

[0051] Establishment of the T2-r conversion relationship: Based on the six-point coupling method of the graph, match the CT A -CT B histogram with the T2 A -T2 B graph to establish the quantitative conversion relationship formula of T2-r pore size, and obtain the nuclear magnetic T2 distribution of the matrix pores and fractures.

[0052] Preferably, as Figure 1 shown, the specific process of the method in this embodiment includes the following steps:

[0053] Step 1, sample preparation.

[0054] Select several (for example, not less than 5 pieces) carbonate rocks with developed fractures to prepare large-size samples (for example, 5-7 cm in length, 6 cm or 10 cm in diameter).

[0055] Step 2, drying.

[0056] Dry the rock samples at 200 °C and let them stand until room temperature, weigh the dry weight m d , and measure the total volume V b .

[0057] Step 3, saturation weighing and porosity measurement.

[0058] After evacuating the rock samples, pressurize (for example, 32 MPa) to saturate with potassium iodide aqueous solution (for example, 10000 ppm); after a period of time (for example, 24 hours), weigh the mass m of the saturated water rock samples s . Calculate the total porosity according to the mass difference between the saturated sample and the dry sample ρ is the density of the aqueous solution.

[0059] Step 4, calculation of the nuclear magnetic T2 spectrum and CT pore size distribution spectrum of the saturated water rock samples.

[0060] 4.1 As Figure 2As shown, the matrix pores of the present invention include two parts: "matrix pore 1" and "matrix pore 2", and the non-matrix pores only have one part, i.e., "fracture 3". Among them, "matrix pore 1" represents the matrix pores lost due to being below the resolution of the CT scanner, and "matrix pore 2" represents the matrix pores identified by CT scanning. The CT scanner is a micron-level CT. Among them:

[0061]

[0062]

[0063]

[0064]

[0065] is the total porosity, which refers to the ratio of the volume of water in the water-saturated rock to the total volume of the rock;

[0066] is the matrix pore porosity, which refers to the amount of matrix pores;

[0067] is the non-matrix pore porosity, which refers to the amount of non-matrix pores where fractures and cavities are located;

[0068] is the CT porosity, which refers to the ratio of the volume of water scanned by CT in the water-saturated rock to the total volume of the rock;

[0069] is the amount of non-matrix pores (denoted as "non-matrix pore 1") where fractures and cavities are located in the CT porosity;

[0070] is the amount of matrix pores (denoted as "matrix pore 2") in the CT porosity;

[0071] is the amount of matrix pores (denoted as "matrix pore 1") that are not obtained by CT scanning due to the influence of resolution.

[0072] 4.2 T2 spectrum of the rock sample in the saturated state scanned by nuclear magnetic resonance (denoted as T2 A ). T2 A reflects the distribution of all pores, including all matrix pores and non-matrix pores, that is, three parts: "matrix pore 1", "matrix pore 2" and "fracture 3", as Figure 2 shown.

[0073] 4.3 CT scan image of the rock sample in the saturated state. Using image recognition technology to draw the pore size r distribution spectrum, denoted as CT A . Affected by the resolution, CT AOnly pores larger than the instrument resolution (about 30 - 50 μm) are reflected, including fractures ("Fracture 3") and some matrix pores ("Matrix Pore 2"), so the CT A belongs to the pseudo - pore distribution. r represents the pore radius, which is a dimensional quantity.

[0074] 4.4 Calculate the CT porosity

[0075] 4.5 Use CT image recognition technology to further distinguish pores and fractures, and calculate the matrix pore porosity and the fracture porosity

[0076] Step 5: Construct the critical state through the gas - flooding water experiment on the rock sample, and extract the critical state evaluation parameters.

[0077] 5.1 The critical state mentioned above refers to the state that after the gas - flooding water experiment, only the matrix pores contain water, while the non - matrix pores where fractures are located do not contain water.

[0078] 5.2 Calculate the water saturation at the critical state by CT, denoted as S C . In actual situations, it is difficult for CT to accurately distinguish the boundary between "Matrix Pore 1" and "Matrix Pore 2". Therefore, combined with the total porosity of the rock sample and the fracture porosity calculate the water saturation S of the rock sample at the critical state C :

[0079]

[0080] 5.2 Critical state evaluation method. According to the water saturation S at the critical state C calculate the critical mass of water m C :

[0081] m C =(m s - m d )*(1 - S C )

[0082] After the rock sample is placed in the holder, apply confining pressure to wrap it. Place a graduated cylinder at the outlet end of the holder to collect the water discharged from the pores. When the water output of the gas - flooding water reaches the critical mass m C , stop the gas - flooding water experiment, otherwise continue the gas - flooding water.

[0083] Step 6: CT and nuclear magnetic resonance scans of the rock sample at the critical state.

[0084] 6.1 Scan the image of the rock sample at the critical state by CT, and draw the pore size r distribution spectrum, denoted as CT B . CT B reflects the pore distribution of "Matrix Pore 2" (belonging to the pseudo - matrix pore distribution).

[0085] 6.2 Nuclear magnetic resonance scan of rock samples in the critical state, denoted as T2 B . T2 B Reflects the matrix pore distribution, including "matrix pore 1" and "matrix pore 2".

[0086] Step 7: Extract fractures by the differential spectrum method.

[0087] 7.1 Subtract the CT pore size distribution spectra of the saturated state and the critical state to obtain the CT distribution of the fracture pore size r A -CT B , and then convert the fracture pore size distribution spectrum into a histogram of the fracture pore size distribution.

[0088] 7.2 Subtract the T2 spectra of the saturated state and the critical state to obtain the T2 time distribution of the fracture pore size T2 A -T2 B .

[0089] Step 8: Establish the T2-r conversion ratio relationship.

[0090] 8.1 According to the six-point coupling method of the graph, match the CT A -CT B histogram with T2 A -T2 B for graph matching, extract the data of 6 intersection points (T2, r), and establish the quantitative conversion relationship formula of T2-r pore size.

[0091] 8.2 In the same coordinate system, plot the nuclear magnetic T2 distributions of the matrix pores and fractures respectively, and mark the pore size r value at the abscissa.

[0092] In summary, the present method can be applied to measure the oil and gas migration ability in fractures and solution pores of strongly heterogeneous carbonate rocks. By measuring the nuclear magnetic T2 spectrum of rocks and combining with micro-CT, the distribution of fractures and solution pores in rock samples can be quantified, the permeability of rocks under different fluid pressures and overburden pressures can be measured, and the constitutive model of rock dynamic permeability can be constructed. This method can effectively extract the distribution position and content of fractures, and compared with the existing methods, it improves the accuracy of quantitative characterization of fractures using nuclear magnetic technology, providing a reliable basis for the evaluation of the fracture structure of strongly heterogeneous carbonate rocks with a large number of developed fractures.

[0093] It should be noted that for the foregoing method embodiments, for the sake of simple description, they are expressed as a series of action combinations. However, those skilled in the art should know that the present application is not limited by the described action sequence, because according to the present application, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily essential to the present application.

Claims

1. A method for calibrating the nuclear magnetic T2 distribution of fractures in strongly heterogeneous carbonate rocks, characterized in that, Including: Calculation of total porosity: Select several carbonate rocks with developed fractures and prepare rock samples, and calculate the total porosity of the rock samples based on the mass difference between the dry-state rock samples and the saturated-state rock samples Scanning of saturated rock samples: The T2 spectrum obtained by nuclear magnetic resonance scanning of saturated rock samples is denoted as T2 A , CT scanning of saturated rock samples and plotting the pore size r distribution spectrum is denoted as CT A ; Construction of critical-state rock samples: Construct critical-state rock samples based on gas flooding experiments and extract evaluation parameters of the critical-state rock samples; Scanning of critical-state rock samples: The T2 spectrum obtained by nuclear magnetic resonance scanning of critical-state rock samples is denoted as T2 B , CT scanning of critical-state rock samples and plotting the pore size r distribution spectrum is denoted as CT B ; Fracture pore size distribution extraction: Based on the difference in the T2 spectra of rock samples in the saturated state and critical state, and the difference in the pore size r distribution spectra, the T2 time distribution T2 of the fracture pore size and the CT of the fracture pore size dimension r distribution are obtained respectively. A -T2 B and the CT of the fracture pore size dimension r distribution A -CT B ; Establishment of T2-r conversion relationship: Based on the graphical six-point coupling method, CT A -CT B histogram and T2 A -T2 B charts are graphically matched to establish a quantitative T2-r pore size conversion relationship formula, and the nuclear magnetic T2 distributions of matrix pores and fractures are obtained.

2. The method for calibrating the nuclear magnetic T2 distribution of fractures in strongly heterogeneous carbonate rocks according to claim 1, wherein The calculation of the total porosity includes: Sample preparation: Select several carbonate rocks with developed fractures and prepare rock samples; Drying: Dry the rock sample and let it stand still until it reaches room temperature, then weigh the dry weight m d , and measure the total volume V b ; Saturated weighing: After evacuating the rock sample, apply pressure and inject saturated potassium iodide aqueous solution. After a period of time, weigh the mass m of the rock sample in the saturated state s ; Calculating the total porosity: Calculate the total porosity based on the mass difference between the dry-state rock sample and the saturated-state rock sample where ρ is the density of the aqueous solution.

3. A method for calibrating the nuclear magnetic T2 distribution of fractures in strongly heterogeneous carbonate rocks according to claim 1, characterized in that, In the scanning of the saturated-state rock samples: The T2 spectrum obtained from NMR scanned saturated rock samples, namely T2 A reflects all pore distributions, including non-matrix pores and all matrix pores; CT scan the saturated rock samples and plot the pore size r distribution spectrum formed, namely CT A Reflect the pore distribution higher than the resolution of the CT scanner, including non-matrix pores and some matrix pores.

4. A method for calibrating the nuclear magnetic T2 distribution of fractures in strongly heterogeneous carbonate rocks according to claim 3, characterized in that, The non-matrix pores are fractures, and the matrix pores include the first type of matrix pores and the second type of matrix pores. The first type of matrix pores represent the matrix pores lost due to being below the resolution of the CT scanner, and the second type of matrix pores represent the matrix pores identified by the CT scanner.

5. A method for calibrating the nuclear magnetic T2 distribution of fractures in strongly heterogeneous carbonate rocks according to claim 4, characterized in that, The scanning of the saturated-state rock samples further includes: Calculating CT porosity based on the pore size r distribution spectrum Distinguish pores and fractures based on CT image recognition technology and calculate the porosity of the second matrix pores and fracture porosity where 6. A method for calibrating the nuclear magnetic T2 distribution of fractures in strongly heterogeneous carbonate rocks according to claim 1, characterized in that, In the construction of the critical-state rock samples, the critical state refers to the state where only the matrix pores of the rock sample contain water, and the non-matrix pores where the fractures are located do not contain water.

7. A method for calibrating the nuclear magnetic T2 distribution of fractures in strongly heterogeneous carbonate rocks according to claim 1, characterized in that, The construction of the critical-state rock samples includes: Calculation of water saturation: Combining the total porosity of the rock sample and the fracture porosity to calculate the water saturation of the rock sample in the critical state Critical state evaluation: Based on the water saturation S of the critical state rock samples C Calculate the critical mass of water m C =(m s -m d )*(1 - S C ), where m d is the mass of the rock sample in the dry state, and m s is the mass of the rock sample in the saturated state; After placing the rock sample in the holder, apply confining pressure to wrap it, place a graduated cylinder at the outlet end of the holder to collect the water discharged from the pores, and stop the water displacement experiment by gas when the water output reaches the critical mass m C , otherwise continue the water displacement experiment by gas.

8. A method for calibrating the nuclear magnetic T2 distribution of fractures in strongly heterogeneous carbonate rocks according to claim 1, characterized in that, In the scanning of the saturated-state rock samples: The T2 spectrum obtained from nuclear magnetic resonance scanning of critical state rock samples, namely T2 B reflects the pore distributions of the first matrix pore and the second matrix pore; CT scan the critical state rock samples and plot the pore size r distribution spectrum formed, namely CT B Reflect the pore distribution of the second type of matrix pores.

9. A method for calibrating the nuclear magnetic T2 distribution of fractures in strongly heterogeneous carbonate rocks according to claim 1, characterized in that, The extraction of the fracture aperture distribution includes: By subtracting the pore size r distribution spectra of saturated state rock samples and critical state rock samples based on the differential spectrum method, the CT of the crack pore size r distribution is obtained. A -CT B , and then it is converted into a bar chart of the crack pore size distribution; By subtracting the T2 spectra of saturated state rock samples and critical state rock samples based on the differential spectrum method, the T2 time distribution of fracture pore sizes, T2, is obtained. A -T2 B .

10. A method for calibrating the nuclear magnetic T2 distribution of fractures in strongly heterogeneous carbonate rocks according to claim 1, characterized in that The establishment of the T2-r conversion relationship includes: Based on the graphical six-point coupling method, CT A -CT B histogram is graphically matched with T2 A -T2 B to extract the data of 6 intersection points (T2, r), and establish a quantitative conversion relationship formula for the T2-r pore size; In the same coordinate system, plot the nuclear magnetic T2 distributions of the matrix pores and fractures respectively, and mark the aperture r value at the abscissa.

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